diff --git a/.travis.yml b/.travis.yml
index 95586dd..ec0171a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,9 +6,7 @@ before_script:
   - nvm install 4.4
   - nvm alias default 4.4
   - npm install
-  - python scraper.py
 script:
-  - node check-uniq-session_id.js
   - sh build.sh
 env:
   - secure: "MA928kGtPidi9F5ciZOogrQnNTZKWPESFq9ew9Mw0wVLu9evcJlFa5WoYXkmOn72hM8qEwoD66R7zb9b+0QS8uHop9QvjG1cjpslzorjE08BU0aMlsx98STPVWB5l8aNOPGE3qhFJmOWm6c+B8lNph61nTMR/4oQ+3+kFvMj4SX9QJ3zZ+VxP/Be5uMkpwySbH9t4rByI4dcvOnwpnsxeuxE7HktNUbuJeAh5nuWuWUgfDrvG2FGgp85zZBQtBTUVAb7ggLNJbdNz6hKOjrVYefqa0bOsoFjbyAtb2vNmfHSsg/xUfBQ/4SSsfYU5jv/uuyp+mdbEb0TLejMNjOCUsIq6bIUe2XgQHJhhHrEtZsUVQEC/1bckxgDFYbmDJcbOQt9j+QAppPkhAoq71IzOnycpmM5zGEZUoOxRIay//Dyg3QyPOJ0Jswce6zKuy8DV5K9aInGBscyY/6Q6Zab7vn0cOYhKEVMSzpKlz4TxGvQm8FGUOqaFFBoxoZlmjzyIeWYqiKRwt7FJgXKEyjbFn8uwt1lZze535eytVgW4Rx4g5QkW6HCQcsQQe0Shqkfb8feDICCw5xPLwUvutrU9/s9HCN/wxpE8nUHhGsODyUl41hCkvocL608wDutgJjhBrQod3wu81Bn8O+ZM/C0XUgvH5LAMxpaMVxg9lMs2Ns="
diff --git a/build.sh b/build.sh
index 2ec0167..2630755 100644
--- a/build.sh
+++ b/build.sh
@@ -5,6 +5,8 @@ set -e
 git config --global user.name "Travis CI"
 git config --global user.email "noreply+travis@fossasia.org"
 
+python scraper.py
+
 # don't continue if no changes
 if git diff-index --quiet HEAD; then
   exit 0
diff --git a/check-uniq-session_id.js b/check-uniq-session_id.js
deleted file mode 100644
index 18dd9fa..0000000
--- a/check-uniq-session_id.js
+++ /dev/null
@@ -1,20 +0,0 @@
-'use strict'
-
-var sessions=require('./out/sessions.json').sessions;
-var map=new Map();
-sessions.map(s => s.session_id).forEach((id, index) => {
-  let seen = map.get(id);
-  if (seen === undefined)
-    map.set(id, [index]);
-  else
-    seen.push(index);
-})
-var has_dupes = false;
-map.forEach((seen, id) => {
-  if (seen.length <= 1)
-    return;
-  has_dupes = true;
-  var dupe_sessions = seen.map(id => sessions[id]);
-  console.log('there are', seen.length, 'duplicates for session id', id, ': ', dupe_sessions);
-});
-process.exit(has_dupes ? 1 : 0)
diff --git a/schedule/generator.js b/schedule/generator.js
index 59e547f..970bcbb 100644
--- a/schedule/generator.js
+++ b/schedule/generator.js
@@ -99,5 +99,18 @@ function transformData(sessions, speakers) {
   return {tracks, days}
 }
 
+function validateSessions(sessionsData) {
+  var ids = sessionsData.map(s => s.session_id)
+  var dups = ids.filter((sid, idx) => ids.indexOf(sid) !== idx)
+  if (dups.length > 0) {
+    console.error('Duplicate session ids: %s', dups.join(', '))
+  }
+  return false
+}
+
+if (!validateSessions(sessionsData.sessions)) {
+  process.exit(1)
+}
+
 const data = transformData(sessionsData, speakersData)
-process.stdout.write(tpl(data))
+// process.stdout.write(tpl(data))